<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=lian, initial-scale=1.0">
    <title>练习</title>
</head>
<body>
    <div style="display: flex;border:2px solid red;height: 300px;width: 500px;">
    <div style="flex: 1;background-color: blue;border:2px; color: white;text-align: center;line-height: 300px;">第一列</div>
    <div style="flex: 1;background-color: rgb(15, 13, 13);;border:2px color white ;">第二列</div>
    <div style="flex: 1;background-color: rgb(22, 245, 78);;border:2px solid white ;">第三列</div>
    </div>

    <div style="position: relative;border:2px solid red;height: 500px;width: 500px;">
        <div style="z-index: 100;position: absolute; right: 0;top: 0;border: 2px solid blue; ;height: 100px;width: 100px;"></div>
        <div style="z-index: 90;position: absolute;right: 0;top: 0;border: 2px solid black; ;height: 100px;width: 100px;"></div>
        <div style="position: absolute;border:2px solid yellow ;right: 0;bottom: 0;height: 100px;width: 100px;"></div>
        </div>
</body>
</html>